Joint Ranging and Data Communication
An emerging IEEE Draft P802.15.4a/D3, April, 2006 standard specifies the use of communication packets for conveying data and determining a range between two radio transceivers. It is likely that the standard will use ultrawideband (UWB), radio signals operating in an unlicensed spectrum of about 3.1 GHz to 4.9 GHz where an actual unlicensed band is 7,500 MHz wide.
The packet exchange sequence is shown in FIG. 1. A transceiver-1 (TRCVR) 140 transmit a data packet 110 to a transceiver-2 150. Upon receiving the data packet 110, the transceiver-2 150 transmits an acknowledgment packet (ACK) 120 to transceiver-140. Optionally, the transceiver-2 150 can also transmit a timestamp packet (TS) 130. The TS packet 130 includes a time the packet 110 was received and a time the packet 120 was transmitted. After exchanging packets 110, 120 and 130, the transceiver-1 can determine the range to transceiver-2 by calculating the time traveled by the data packet 110.
As shown in FIG. 2, the IEEE standard IEEE Draft P802.15.4a/D3, April, 2006, specifies a structure of the data range packet 110 that is used for both data communication and ranging. The data packet 110 includes synchronization header (SHR) 200, physical (PHY) header 210 and payload 220. The SHR header 200 includes a preamble 230 and start of frame delimiter (SFD) 240. The preamble 230 includes repetitions of a perfectly balanced ternary sequence (PBTS) Si250.
As shown in FIG. 3, the IEEE Draft P802.15.4a/D3, April, 2006 specifies eight different sequences of length 31 codes for Si250.
As shown in FIG. 4A, the Si250 is a sequence includes ternary symbols of +1 420, −1 430, or 0 440, and has a perfect periodic autocorrelation 450 property in a sense that side-lobes between the autocorrelation peaks 460 are zero as shown in FIG. 4B.
As shown in FIG. 4C, the symbol Si250 and a pulse repetition interval (PRI) 410 are input to a pulse shaper 470 before transmission. The pulse shaper 470 outputs a continuous time waveform s(t) 480, which can be expressed as follows for the preamble 230
                                          s            ⁡                          (              t              )                                =                                    ∑                              k                =                1                                            L                i                                      ⁢                                                            S                  i                                ⁡                                  (                  k                  )                                            ⁢                              p                ⁡                                  (                                      t                    -                                          k                      .                      PRI                                                        )                                                                    ,                            (        1        )            where Li indicates the length of Si and p(t) is the ultra-wideband pulse waveform. Each pulse in s(t) is separated from the next pulse by the PRI 410. Each peak of the autocorrelation of s(t) is separated from the next peak by one symbol duration Ts 
                              T          s                =                              L            i                    ·          PRI                                    (        2        )            The symbol duration Ts corresponds to an interval of 31 samples 260 (Li=31).
Conventional Radar
US Publication 20020109624 describes a system including a sensor unit having at least one antenna for transmission of a signal into an area. Any intrusion in the area is detected upon a change in the waveform received by the antenna. A received signal is transmitted from the sensor unit to a control unit to determine the movement of an intruder. Utilization of a plurality of sensor units allows the user to obtain additional information on the speed and location of the intruder. Additionally, as with conventional security systems, that prior art system can provide an electrical signal to activate a sound and/or light transceiver to attract the attention of the intruder and warn others of the intruder's presence. That system only functions as an ultra-wideband radar and does not provided for data communication.
US Publication 20060017608 describes a method and system for reducing clutter interference in a radar-responsive tag system. A radar device transmits a series of linear-frequency-modulated pulses and receives echo pulses from nearby terrain and from radar-responsive tags that may be in the scene. Tags in the vicinity of the radar are activated by the pulses. The tags receive and re-modulate the radar pulses. Tag processing reverses the direction, in time, of the received waveform's linear frequency modulation. The tag retransmits the re-modulated pulses. The radar uses a reversed-chirp de-ramped pulse to process the tag's echo.
Passive Radar
Passive radar detects changes in an propagation environment due to a presence of a target object. In a typical passive radar system, passive sensors receive signals emitted by target objects.
U.S. Pat. No. 6,275,283 uses passive ranging to a source with a known spectral emission to cue active radar system. Optical multiple passive systems (PS) are employed. The PS provides range and rate information to an active radar system. By this way, the active radar can achieve better resolution with fewer transmissions.
Another passive system is described in U.S. Pat. No. 5,444,451. Passive means for single site radio location, which uses a single passive radar transceiver with a couple of sensors to determine the location of the target object. By measuring the inter-sensor delay times, the direction of arrival (DOA) of the target object's signal can be determined for positioning purposes.
US Publication 20040257270 describes a passive radar receiver with an array of antennas for an OFDM received signal comprising frames of symbols, each emitted on coded orthogonal carriers. After formatting received signals into digital symbols, dummy signals from dummy OFDM emitters at different distances from and in different directions relative to the receiver are generated and added to the signals picked up by the antennas. The modified received signals are filtered by means of inverse covariance matrices in order to eliminate at least unwanted zero Doppler effect signals and to provide an isotropic reception diagram without blind sector of direct path being generated and by detecting mobile target objects along the direct path.
U.S. Pat. No. 5,323,161 describes a method of assessing radar pulses. A passive radar system can distinguish pulses coming from a target object from pulses from other sources. Confidence values are calculated for the received pulses to identify the pulses of the target object without the need for any reference pulse. By this technique, a certain target object can be detected from its pulse structure.
U.S. Pat. No. 5,280,294 uses passive mono-pulse ranging to a non-cooperative emitter and non-emitting object. In a passive radar system, the range to a target object and to non-cooperative scanning radar is estimated. The PS component consists of a passive antenna array with beam-forming and a switching matrix to provide separate outputs for each of the object and emitter.
US Publication 20050275582 describes a bi-static continuous wave radar system and a related method for detecting incoming threats from ballistic projectiles. The radar system includes a remote source of RF illumination. A first receiving channel acquires direct path illumination from the source and provides a reference signal. A second receiving channel acquires a scatter signal reflected by a projectile. A processor coupled to each receiver corrects scatter signal Doppler offset induced by relative source motion, isolates narrowband Doppler signals to derive signatures characteristic of the projectile, and by executing appropriate algorithms, compares the derived signatures to modeled signatures stored in memory. If the comparison yields a substantial similarity, then the processor outputs a warning signal sufficient to initiate defensive countermeasures.